Various types of seal assemblies and running tools have been devised for sealing a casing annulus. A casing hanger may be positioned within the wellhead, and a running tool may be used to actuate the seal assembly carried on the casing hanger and thereby seal with the casing hanger.
For various reasons, a casing hanger within the wellhead may move axially upward, particularly when the wellhead is part of a production system wherein downhole fluids at elevated temperatures thermally expand the casing string and thus exert a substantial upward force on the casing hanger. Since the casing hanger seal is intended for sealing at a particular location on the wellhead, upward movement of the casing hanger and the seal assembly is detrimental to reliably sealing the casing annulus.
A seal assembly for a casing hanger in a wellhead is disclosed in U.S. Pat. No. 5,287,925. Another type of seal assembly between a wellhead and a tubing hanger seal is disclosed in U.S. Pat. No. 6,598,680. U.S. Pat. No. 6,705,615 discloses yet another version of a seal assembly for use in a wellhead, and U.S. Pat. No. 6,969,070 discloses improvements in a seal assembly. A pressure actuated seal assembly and running tool are disclosed in U.S. Pat. No. 7,096,956.
The disadvantages of the prior art are overcome by the present invention, an improved wellhead seal assembly and running tool are hereinafter disclosed.